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Sugars (eg, glucose, galactose, fructose, maltose, lactose, and pentose) are characterized as reducing substances based on their ability to reduce cupric ions to cuprous ions.
Fecal reducing substances may be increased in carbohydrate malabsorption syndromes.
Diagnosing intestinal malabsorption in children
Assisting in the differentiation between osmotic and nonosmotic diarrhea
Screening test for:
-Diarrhea from disaccharidase deficiencies, (eg, lactase deficiency)
Normal: <0.25 g/dL (trace)
Suspicious: 0.25 to 0.50 g/dL (grade 1)
Abnormal: >0.50 g/dL (grade 2-4)
A number of other compounds also are capable of reducing cupric ions to cuprous ions and can cause false-positives.
Ambient transport temperatures result in growth of bacteria. Bacteria consume reducing substances, which can result in false-negative results, so ambient specimens are rejected.
This test has poor sensitivity for oligosaccharides and poor sensitivity from diaper stools because fluid is reabsorbed into the diaper. Testing of only the solid portion of the stool will give a falsely-low reading since the liquid portion of the stool contains the water-soluble sugars.
Possible interferences include: salicylates, penicillin, choral hydrate, menthol, phenol, streptomycin, para-aminosalicylic acid, isoniazid, ascorbic acid, cephalosporins, and probenecid.
Negative or trace
Todd S: Archives of disease in childhood: differentiation of osmotic and secretory diarrhea by stool carbohydrate and osmolar measurements. In Clinical Diagnosis and Management by Laboratory Methods. Vol 77. 20th edition. Edited by JB Henry, FR Davey, CJ Herman, et al. Philadelphia, Saunders, 2001, pp 201-205